Quote from: erioladastra on 08/26/2011 05:29 pmQuote from: simonbp on 08/26/2011 04:03 pmQuote from: Ronsmytheiii on 08/26/2011 01:16 pmAs has already been stated before, there were real concrete reasons for needing a window in the docking process in the first place. Except there isn't. As I said, cameras are small and cheap, so you can put four fully redundant cameras, each with its own separate string to the control panel, and it would still have less than 1/10 the mass impact on the vehicle as forward-looking window. And frankly, if they loose any major sensors during flight, docking will be aborted anyways, regardless of any windows.Cameras are not neccessarily better. Yes, cameras *may* have less mass, but you trade that against power and data transfer for the camera plus an extra crew display. So you might not be less mess and you are trading against critical items like power and increasing the complexity of the system (which means cost, risk) etc.Yeah, the trade could go different ways. But don't you think it should be up to the commercial crew provider to find the most cost-and-performance-optimal solution that meets the required level of safety?
Quote from: simonbp on 08/26/2011 04:03 pmQuote from: Ronsmytheiii on 08/26/2011 01:16 pmAs has already been stated before, there were real concrete reasons for needing a window in the docking process in the first place. Except there isn't. As I said, cameras are small and cheap, so you can put four fully redundant cameras, each with its own separate string to the control panel, and it would still have less than 1/10 the mass impact on the vehicle as forward-looking window. And frankly, if they loose any major sensors during flight, docking will be aborted anyways, regardless of any windows.Cameras are not neccessarily better. Yes, cameras *may* have less mass, but you trade that against power and data transfer for the camera plus an extra crew display. So you might not be less mess and you are trading against critical items like power and increasing the complexity of the system (which means cost, risk) etc.
Quote from: Ronsmytheiii on 08/26/2011 01:16 pmAs has already been stated before, there were real concrete reasons for needing a window in the docking process in the first place. Except there isn't. As I said, cameras are small and cheap, so you can put four fully redundant cameras, each with its own separate string to the control panel, and it would still have less than 1/10 the mass impact on the vehicle as forward-looking window. And frankly, if they loose any major sensors during flight, docking will be aborted anyways, regardless of any windows.
As has already been stated before, there were real concrete reasons for needing a window in the docking process in the first place.
After examination of multiple DRMs and requirement documents, high-level driving requirements were determine to be:- The avionics architecture shall be human-rateable,- The avionics architecture shall, at a minimum, be fail-operational after one arbitrary fault,- The avionics architecture shall, at a minimum, be fail-safe (for abort initiation) after a second arbitrary fault,- The avionics architecture shall be highly reliable to meet Loss of Crew (LOC) and Loss of Mission (LOM) for various NASA missions.
Reliability analysis showed all architectures except one were at a reliability level of least0.9999 for short duration (i.e. 24 hour, preflight plus time to orbit) reliability but variedsignificantly (0.3576 to 0.6669) if a longer duration (i.e. 9 month, departure stage forMars DRM) was needed. For all architectures, the flight computers were the largestcontributor to failure. Reliability analysis assumed all architectures to be 1-fault tolerantby design but the number of 2-fault cases varied from 21 to 160 depending on thechosen architecture. The reliability of the architectures is related directly to the level ofcross-strapping in the various architectures.
Why the heck would they exclude a hatch window?Does NASA want an affordable commercial crew program, or not?
Quote from: Robotbeat on 08/20/2011 08:06 pmWhy the heck would they exclude a hatch window?Does NASA want an affordable commercial crew program, or not? It does NOT mean there is no hatch window....
They mean the hatch window does not count for the purposes of this requirement.
QuoteThey mean the hatch window does not count for the purposes of this requirement. And why the heck not?
Maybe the hatch windows don't count since MPCV was already made that way?
Quote from: DaveH62 on 09/02/2011 07:30 pmMaybe the hatch windows don't count since MPCV was already made that way? Maybe indirectly but it couldn't be justified simply on the grounds that MPCV just happens to be built that way.I expect MPCV and CST-100 have windows in the places they do because there are/were NASA requirements they had to satisfy for the original CxP/OSP/whatever programs. Those requirements probably fall under the "crew health and safety" or "mission safety and success" categories.NASA attempting to now relax those classes of requirements for CCP could be extremely difficult, and would likely fuel the "commercial isn't safe" crowd.
Part of the challenge with long term planning horizons, is the ability to create alternate scenarios based on opinion, rather than designs facts. It is very hard to prove that a camera system could be 99.999% reliable. It is not a solid state solution, like a window, so it can malfunction. A camera should provide better visibility and provide more functional value, but it could have issues. That said, it is difficult to imagine a scenario where adequate redundancy could not be built in to provide at least 5 9s. It also seems likely that an event that would damage cameras, camera wiring, or associated computers taking the video feed, would impact either windows or the avionics of the ship as a whole. If something smashed a camera outside the ship, then that would be safer than something smashing a window. You could still turn around and go home.
Significant changes to 1130 requirements- Manual Control - Abort Effectiveness- Mission Duration- Loss of Crew/Loss of Mission- Health and Medical Requirements- Emergency Entry- Failure Tolerance
•Updated the following mission and system capabilities:–Support multiple back-to-back launch opportunities in a two week period in order to accomplish a single mission
•Updated phasing time consistent with CCT-REQ-1130–The CTS spacecraft will nominally be capable of transporting NASA crew to the ISS within 24 hours of launch
Quote•Updated the following mission and system capabilities:–Support multiple back-to-back launch opportunities in a two week period in order to accomplish a single missionThis means that if it has to scrub a launch it has to be able to recycle within two weeks?
Quote•Updated phasing time consistent with CCT-REQ-1130–The CTS spacecraft will nominally be capable of transporting NASA crew to the ISS within 24 hours of launchThis means that it has to have the capability of a fast mission, but might elect a slower orbital profile for better performance?
- 24 hours is a “design point” to accommodate ISS phasing- Rationale addresses Industry recommendation to allow operational flexibility in mission-to-mission rendezvous timeline
My impression from reading is that they are pointing to a taxi model. Does that seems right or I am reading too much between the lines?
Quote from: baldusi on 10/04/2011 09:23 pmMy impression from reading is that they are pointing to a taxi model. Does that seems right or I am reading too much between the lines?It seems more like a rental car model to me. With a taxi, the driver and vehicle typically don't stay with you for the duration once you reach your destination (it also appears NASA crew will be driving).
"No mention of windows."Updated to be two (or meet the intent) class A science windows with no electronic observation for piloting or blockage of windows. So got mught tighter. However, likely to change.